Congestive heart failure (CHF) in the United States has a prevalence of approximately 5.8 million people and an incidence of approximately 550,000 people annually. CHF is a rapidly growing medical problem. CHF can be categorized as either systolic heart failure (SHF) or diastolic heart failure (DHF). The estimated direct and indirect cost of CHF in the United States for 2009 is $37.2 billion. CHF is the primary reason for 12-15 million office visits and 6.5 million hospital days each year. CHF is also thought to be the cause of at least 20 percent of all hospital admissions among patients older than 65. Over the past decade, the rate of hospitalizations for heart failure has increased by 159 percent. About half of all patients with CHF have DHF. DHF has an annual mortality of ˜10%.
FIG. 1 illustrates a cross sectional view of a representation of a heart 10. In a normally functioning heart, oxygenated blood enters the heart 10 via pulmonary veins 12 into the right atrium 14. During diastole the heart muscles relax allowing the left atrium 16 to fill with the oxygenated blood. During systole, the heart muscle contracts reducing the volume of the left atrium 16 and causing oxygenated blood to flow through the aortic valve 18 into the aorta 20 for circulation through the body.
The hearts of patients with diastolic dysfunction can contract normally or even with hyperdynamic function. However, in patients experiencing DHF, the part of the cardiac cycle that involves diastole is abnormal as the left ventricle cannot relax or expand sufficiently. The inability of the left ventricle to fully relax results in sub-optimal filling of the left ventricle with blood.
In particular, diastolic dysfunction is determined by two factors: 1) active myocardial relaxation, primarily affecting early diastole; or 2) passive elasticity or distensibility of the left ventricle, primarily affecting late diastole.
The abnormal filling of the ventricles in DHF results in limited cardiac output, especially during exertion. As a result, for any given ventricular volume in a heart with DHF, ventricular pressures are elevated, with backup in the circulatory system, leading to pulmonary congestion and edema identical to those seen in patients with SHF. Symptomatically, patients may immediately feel short of breath. This dysfunction can ultimately lead to multiorgan dysfunction and death.
There are currently no approved devices for diastolic dysfunction. Additionally, pharmaceutical intervention has not yet shown to improve outcomes in this population.